1. Field of the Invention
The present invention relates to an apparatus which can process data at a high speed especially an apparatus for processing data for the purpose of forming an image.
2. Description of the Prior Art
Hitherto, in data processing apparatuses such as a printer or the like of the type whereby sentences and image information are outputted as bit images, it is required to develop the foregoing information at arbitrary locations in a page on a bit unit basis. However, the readout from or writing in a memory is generally performed on a plurality of bit unit basis such as a four- or eight-bit unit from viewpoints of the processing speed or efficiency of a CPU. Therefore, a method has been adopted whereby data is preliminarily shifted on a bit unit basis by a register in a CPU and thereafter it is stored in the memory on the basis of a unit of four or eight bits.
However, the foregoing method has a drawback such that the data processing speed is slow in high speed printers such as, in particular, a laser beam printer (LBP). In addition, in many cases, a problem on realization of high processing speed is caused in various kinds of data processing apparatuses using a microprocessor or the like as well as the printers.
On one hand, in output apparatuses such as a laser beam printer (LBP) or the like of the type in which information such as code data or the like which is transmitted from a host computer or the like is developed as a bit image in a random access memory in the apparatus and thereafter this bit image is read out and outputted, it is necessary to overlappingly write it into the random access memory.
Namely, for instance, in case of outputting a pattern of FIG. 1(a), a pattern of FIG. 1(b) is once written and thereafter a pattern of FIG. 1(c) is overlappingly written. It is very difficult to discriminate the pattern to be written to see if it is merely written or overlappingly written, so that there is a necessity to preliminarily clear the random access memory in which the pattern is to be written.
Therefore, with regard to the portion where a pattern was completely developed in the random access memory and has been again read out and printed, it is necessary to clear that portion at every time.
However, the above-mentioned operation can be realized by the operation of only the CPU if the sentence output apparatus is of the low speed type and the processing speed of the CPU can sufficiently cope with such a low output speed. However, the low speed operation of the CPU is useless in high speed printers such as a laser beam printer or the like and, therefore, the parallel processes are ordinarily executed together with the CPU by use of a high speed subprocessor. This causes a drawback such that the cost of the overall processing apparatus becomes very high.
On the other hand, recently, an LSI is installed in a data processing apparatus and multi functions are being realized. It is becoming a general method that with an increase in capacity of the RAM, the content of one kind of RAM is divided into a data buffer, stack, flag area or the like and is used.
However, as described above, in the laser beam printer or the like in which sentence information such as code data or the like which is transmitted from a host computer or the like is developed as bit thereafter the bit images are read out and outputted, it is considered to be effective to provide a data conversion writing device such that the bit image is shifted and overlappingly written into the data buffer, such as table format + data because of necessity of the high speed process.
However, in case of using the same RAM as a flag or stack, the operation of the data conversion writing device causes the content of the flag or stack to be changed; therefore, there is a drawback such that this electronic equipment cannot execute a desired function.